Aluminum substrate disk having silica gel coating

ABSTRACT

A magnetic recording disk having a silica gel layer disposed between an aluminum substrate and a magnetic recording layer.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional application of U.S. applicationSer. No. 10/077,200 filed on Feb. 15, 2002, which claims priority toU.S. Provisional Application No. 60/269,517, filed on Feb. 16, 2001.

TECHNICAL FIELD

[0002] This invention relates to a patterned medium having land areasfor storing data and trough areas for inhibiting storage of data, and touse of the patterned medium with a read wide/write narrow recordinghead.

BACKGROUND

[0003] A magnetic disk drive is a digital data storage device thatstores digital data on magnetic medium known as a disk. The disk, ingeneral, comprises a plurality of tracks for storing the digital data.Data is stored on the tracks of the disk in the form of magneticpolarity transitions induced into a magnetic layer covering the disk.

[0004] During operation of the disk drive, the disk is rotated about anaxis by a spin motor at a substantially constant angular speed. Toperform a transfer of data with the disk, a transducer, known as arecording head, is centered above a track of the rotating disk. Oncecentered, the head can be used to transfer data to the track (during awrite operation) or to transfer data from the track (during a readoperation). During writing, for example, a write current is delivered tothe centered head to create an alternating magnetic field in a lowerportion of the head that induces magnetic polarity transitions onto thetrack. During reading, the centered head senses magnetic fieldsemanating from the magnetic polarity transitions on the moving track tocreate an analog read signal representative of the data thereon.

[0005] The recording head may be a dual element head having a readelement for performing a read operation and a write element forperforming a write operation. It is known to make the read element widerthan the write element provided that the write element contains erasebands on its edges to “erase” old data from a track on the disk andthereby prevent the read element from sensing that old data. Thisconfiguration is described in U.S. Pat. No. 5,940,250 (McNeil et al.),the contents of which are hereby incorporated by reference into thisapplication as if set forth herein in full.

DESCRIPTION OF DRAWINGS

[0006]FIG. 1 is a diagram illustrating an offset between a read elementand a write element in a dual element recording head and the effect theoffset has when positioning the head over various tracks.

[0007]FIGS. 2A, 2B and 2C illustrate a write operation to a track, asecond subsequent write operation to the same track, and using a dualelement recording head having a read wide/write narrow architecture.

[0008]FIG. 3 is a cross-sectional, side, perspective view of a patternedmedium and a write element of a read wide/write narrow dual elementrecording head.

[0009]FIG. 4 is a cross-sectional, side view of the patterned medium,illustrating components that make up the patterned medium.

[0010]FIG. 5 is a top view of the patterned medium and the relationshipof the patterned medium to a read element and a write element of a dualelement recording head.

[0011]FIG. 6 is a cross-sectional, side, perspective view of a patternedmedium that contains data islands in its data tracks.

[0012]FIG. 7 is a top view of a magnetic recording medium comprised oflands for storing data and troughs having steps for storing servoinformation.

[0013]FIG. 8 is a cross-sectional, side view of the magnetic recordingmedium of FIG. 7.

[0014]FIG. 9 is a block diagram of a magnetic recording system thatincludes a magnetic recording medium having servo information writteninto troughs of a patterned medium.

[0015] Like reference numerals in different figures indicate likeelements.

DETAILED DESCRIPTION

[0016] During read and write operations in a disk drive, a recordinghead is maintained in a centered position above a desired track in aprocess known as track following. When using a dual element head, thisprocess entails centering the write element during a write operation andcentering the read element during a read operation. For various reasons,the write element of a dual element head is not always centered on atrack when the corresponding read element is centered on the track andvice versa.

[0017]FIG. 1 is a top view illustrating a dual element recording head 16in various positions above a disk 18. That is, the figure showsrecording head 16 above a first track 20 at the outer diameter (O.D.) ofdisk 18, above a second track 22 at the inner diameter (I.D.) of disk18, and above a third track 24 at a middle diameter (M.D.) of disk 18.It should be appreciated that three heads are shown in FIG. 1 forcomparison purposes only and that, in general, there will be only onehead above each disk surface in the drive. It should also be appreciatedthat the dimensions illustrated in FIG. 1 are exaggerated forillustration purposes.

[0018] As shown in FIG. 1, recording head 16 is located at the end of anactuator arm 40 that carries recording head 16 above the surface of disk18. Actuator arm 40 pivots about a pivot point (not shown) so that theangle that arm 40 makes with each track centerline varies across thesurface of the disk. This angle is known as the skew angle. Recordinghead 16 includes a read (RD) element 26 having a center defined bycenterline 30 and a separate write (WR) element 28 having a centerdefined by centerline 32. As illustrated, read element centerline 30 ispurposely offset in a lateral direction from write element centerline32. Because of the combined effect of the skew angle and the offsetbetween the read and write elements, read element 26 and write element28 are usually not centered on the same track of disk 18 at the sametime. That is, if one of the two elements is centered on a particulartrack, the other is generally off-center by a certain amount.

[0019] To perform the track following function, a servo system (notshown) is generally implemented that uses feedback information, readfrom disk 18 by read element 26, to properly position recording head 16.Because read element 26 provides the feedback information to the servosystem, the system will center read element 26, rather than writeelement 28, if additional information is not supplied to the servosystem. During a write operation, therefore, a compensation value isdelivered to the servo system to center write element 28, if additionalinformation is not supplied to the servo system. The compensation valuedelivered to the servo system generally varies across the surface of thedisk based on the combined effect of the skew angle and the offsetbetween the elements.

[0020] Even when a servo system is being used by the disk drive toposition the head, a certain amount of misalignment can exist betweenthe centerline of an element of the recording head and the centerline ofthe desired track during normal disk drive operation. This misalignmentis caused by various factors such as, for example, spindle run out,resonance and disk flutter, thermal track shift, head settling, actuatorinteractions, improper servo writing, and others. For a particular diskdrive, the misalignment between the head element and the track duringnormal track following operations is specified by a trackmisregistration (TMR) value. The TMR value represents the maximum rangeof element misalignment that is probable during normal track followingoperations of the disk drive. That is, while the disk drive is trackfollowing, it is probable that the element centerline will be somewherewithin the range specified by the TMR value and improbable that the headwill be outside of this range. In general, the TMR is a statisticallyderived value based on past observation in similar or identical diskdrive systems.

[0021] One type of dual element recording head is a magnetoresistivehead that includes a magnetoresistive (MR) read element and a separatewrite element that is usually inductive. MR read elements include asmall piece of magnetoresistive material having a variable resistivitythat changes based on an applied magnetic field. That is, as themagnetic field applied to the material increases, the resistivity of thematerial, in general, decreases. In practice, the MR material is heldnear the desired track as a substantially constant current is runthrough the material. The magnetic field variations produced by themagnetic transitions on the rotating track change the resistance of themagnetic material, resulting in a variable voltage across the materialthat is representative of the data stored on the disk (i.e., a readsignal). MR read elements have gained much popularity in recent years asthey typically generate read signals having considerably higher voltagethan those generated by inductive read elements.

[0022] Dual element heads of the past utilized a write wide/read narrowapproach. It has been determined, however, that this approach results inproblems associated with a nonlinear servo position signal transferfunction. Accordingly, read wide/write narrow dual element heads weredeveloped. In a read wide/write narrow dual element recording head, thewidth of the read element exceeds the width of the write element.

[0023] FIGS. 2A-2C illustrate the use, with a non-patterned medium, of adual element recording head 42 having a read wide/write narrowconfiguration. In this context, a non-patterned medium is a recordingmedium, such as a magnetic disk, that is substantially smooth on itsrecording surface. That is, a non-patterned medium does not contain thephysically imprinted land and trough areas described below.

[0024] Dual element recording head 42 includes a write element 44 havinga write width (W) and read element 46 having a read element width (R),where the read width is greater than the write width. Recording head 42also includes a read element centerpoint 48 and a write elementcenterpoint 50 that are substantially laterally offset from one anotherwith respect to direction of travel 52 of the recording head. Boundarylines 54A, 54B represent the TMR boundaries for data track 56.

[0025] In addition, write element 44 includes erase bands 58A and 58Bfor creating magnetic erase bands on either side of the data writtenonto track 56 by write element 44. The magnetic erase bands are formedof magnetic flux at the edges of write element 44. This flux is inherentin all write elements and may be increased or decreased to increase ordecrease, respectively, the size of the magnetic erase bands. Althoughthe operation of the magnetic erase bands is not strictly necessary forthe present invention, a description thereof may aid in understandingbenefits provided by the patterned media described below.

[0026]FIG. 2A illustrates a first write operation to track 56 using dualelement recording head 42. During a first write operation, write element44 is centered on the left TMR boundary 54A and therefore writes firstdata 60 off-center to the left on track 56. Magnetic erase bands 58A,58B of write element 42 create first erase strips 62A, 62B. In thiscontext, erase strips 62A, 62B comprise areas of track 56 where noreadable data is stored.

[0027]FIG. 2B illustrates a second, subsequent write operation to track56. During the second write operation, write element 44 is centered onright TMR boundary line 54B and, therefore, writes second data 66 ontrack 56 off-center to the right. Also, erase bands 58A, 58B of writeelement 44 create second erase strips 68A, 68B on either side of seconddata 66 during the second write operation. As illustrated, second erasestrip 68A on the left of data 66 erases any of first data 60 that wouldotherwise have remained on track 56 after the second write operation.Thus, during the subsequent read operation of FIG. 2C, read element 46will not sense first data 60 on track 56.

[0028] Instead of, or in addition to, providing magnetic erase bands onthe write element, effective erase bands may be physically formed (e.g.,stamped) onto a patterned medium. A patterned medium is a magneticstorage device, such as a magnetic disk, that contains land areas(“lands”) and trough areas (“troughs”). Referring to FIG. 3, lands 70(70 a-70 c) are raised areas of patterned medium 72 and the troughs 74(74 a, 74 b) are indentations located between lands 70.

[0029] Referring to FIGS. 3 and 4, patterned medium 72 is a magneticdisk comprised of a substrate 76 and a polymer layer 78 disposed atopthe substrate. One example of a polymer that may be used is plastic;however, other types of polymers may be used instead of, or in additionto, plastic. Instead of using a polymer layer, a layer may be used thatis comprised of a glazing compound containing silica that is processedin its uncured state and subsequently cured at a high temperature. Thefollowing article, the contents of which are incorporated herein byreference, describes a process for making such a layer: “Fine PatterningOn Glass Substrates By The Sol-Gel Method”, Tohge et al., Journal ofNon-Crystalline Solids 100 (1988), pgs. 501-505. Examples of substratesthat may be used for substrate 76 include, but are not limited to, glasssubstrates, NiP-clad aluminum alloy substrates, glass-ceramicsubstrates, and titanium substrates. A magnetic layer (not shown) isdeposited over the polymer (or silica/Sol-Gel) layer, either before orafter stamping of the pattern. The land/trough pattern is stamped ontolayer 78 of the medium using a mold that holds an inverse of theland/trough pattern.

[0030] The troughs have a depth relative to the recording head and/orthe lands that is sufficient to inhibit storage of data in the troughsat the frequency that the data is written. During a write operation, theread wide/write narrow recording head is positioned over the lands suchthat the lands are substantially covered by both the read and writeelements. The read element is wider than the write element and the writeelement is at least as wide as the lands and may be wider.

[0031] During writing, the recording head “flies”, i.e., moves, over thepatterned medium. The troughs are sufficiently far from the recordinghead to inhibit, and preferably to prevent, writing of data inside thetroughs. That is, the troughs are far enough away from the recordinghead to prevent the flux transitions caused by the write element fromaffecting the magnetic polarity of the areas of the medium defined bythe troughs. The lands, however, are sufficiently close to the recordinghead to permit magnetic writing of data thereon.

[0032] Thus, when data is written to patterned medium 72, the landsconstitute the data tracks and the troughs constitute effective erasebands. On a circular magnetic disk, the lands and troughs may be formedas alternating concentric circles (taking into account any servo spokesformed onto the magnetic disk). The troughs isolate the lands (i.e., thedata tracks) from one another, resulting in data tracks that are definedclearly both physically and magnetically. Alternatively, the lands andtroughs may be alternated spirals. Other track configurations also maybe used.

[0033]FIG. 5 shows a top view of the patterned medium of FIGS. 3 and 4.As shown in FIG. 5, a recording head 80, containing a read element 82and a write element 84, is positioned over a land 70 a (a data track).In one pass, write element 84 writes data to the land. Data is not,however, written to troughs 74 a and 74 b that are adjacent to land 70 abecause write element 84 is positioned vertically (arrow 73 in FIG. 3)too far above the troughs to induce magnetic transitions in the troughsat the frequency at which the data is written.

[0034] Thus, if new data is written to land 70 a, e.g., on a second passby write element 84, there should be no residual data from the firstpass on the land 70 a or in the troughs 74 a and 74 b. Accordingly, whenread element 82 reads data from track 70 a, only data from the secondpass will be read. To achieve these advantages, constraints may beplaced on the widths of the read element and the write element.

[0035] Referring to FIG. 5, constraints for the width 88 of read element82 and the width 90 of write element 84 are determined as follows. Theminimum width (R_(min)) of the read element may be constrained asfollows:

R _(min) =TW,

[0036] where TW is the width of track 70 a (i.e., lands) formed ontopatterned medium 72. The width of the read element should not be lessthan the track width, i.e., R≧TW. The minimum width of the write element(W_(min)) may be constrained as follows:

W _(min) =TW+WTMR,

[0037] where TW is as defined above and WTMR is an amount of writeelement misregistration (i.e., the amount of TMR that may occur withrespect to write element 84).

[0038] The read element TMR (RTMR) is the amount of TMR that may occurwith respect to read element 82. The minimum off-track registrationcapacity of the recording head (OTRC_(min)) is defined as follows

OTRC _(min)=(R−TW)/2=RTMR.

[0039] Track spacing (Ts) is defined as the sum of TW and the gap (GAP)between adjacent tracks, such as 70 a and 70 b, or

Ts=TW+GAP.

[0040] Squeeze (SQ) is the amount by which the gap between adjacenttracks is reduced when write element 84 extends beyond the width TW oftrack 70 and into trough 74 a. Squeeze is defined as follows

SQ=WFG+Overshoot,

[0041] where WFG is the “Write Fault Gate”, which corresponds to apredetermined limit that a head can write when it is off-track, themagnitude of which is determined by servo position information, and“Overshoot” is the amount by which the recording head exceeds the WFGwhen writing during seeking or during a shock event. Overshoot is aconstant that is determined empirically based on parameters of the diskdrive, and especialy by the servo bandwidth.

[0042] The OTRC under a squeeze condition (O_(SQ)) is defined as followsby setting the squeeze margin to zero

O _(SQmargin) =Ts−TW/2−W _(max)/2−SQ,

[0043] where W_(max) is the maximum width of write element 84 and TS, TWand SQ are as defined above. Setting O_(sqmargin) to zero andsubstituting “TW+GAP” for “Ts”, results in the following

O=TW+2GAP−TW/2−W _(max)/2−SQ.

[0044] Solving for W_(max) results in

W _(max) =TW+2GAP−2SQ.

[0045] The maximum width of the read element (R_(max)) may be definedbased on the structure of the patterned medium and the dual elementrecording head as

R _(max) =TW+2GAP−2RTMR.

[0046] Using a patterned medium, the read width of the read element canbe increased significantly relative to read elements used withnon-patterned media. One reason for this is that the troughs prevent olddata from being written outside of the data track, making it possible toincrease the width of the read element without fear of the read elementsensing substantial amounts of old data. For example, in one embodiment,in which the TMR and track width tolerances scale at 110 tracks-per-inch(TPI), the width of the read element can be more than doubled, from 0.10microns (μm) to 0.22 μm. Increasing the width of the read element alsoprovides signal-to-noise (SNR) ratio advantages. That is, the amount ofvalid data increases relative to noise from, e.g., old data. Forexample, it is possible to obtain a six (6) decibel (db) advantage inSNR using a patterned medium and read wide/write narrow recording head.

[0047] The invention is not limited to the above embodiments. The datatracks on the patterned medium may have the same or a different track orbit density at an inner diameter of the magnetic disk than at an outerdiameter of the magnetic disk. For example, the data tracks may have ahigher density at the inner diameter than at the outer diameter, i.e.,Ts may vary.

[0048] The data tracks may include data “islands”, as shown in FIG. 6.These data islands 100 each hold a block of data, which may be one bitor multiple bits, and are isolated/separated from one another by troughs102 within the data track itself. As is the case with troughs 74 betweenthe data tracks, the troughs 102 between data islands 100 have a depthrelative to the recording head and/or data islands that is sufficient toprevent magnetic writing of data to the trough areas 102 (the depth oftroughs 74 and 102 need not be the same). This configuration provides anadded benefit in that it reduces the amount of noise (e.g., noisebetween tracks) that is sensed by the read element.

[0049] Servo information (e.g., position error information) may also bestored on the lands. The servo information may be stored on the landsusing servo bursts at the start of each sector of a magnetic disk. Forexample, referring to FIGS. 4 and 5, the servo information may berecorded onto two or more sub-tracks (e.g., portions of tracks 70 a, 70b and/or 70 c) in a specific sector of the magnetic medium. Referring,alternatively, to FIG. 6, the servo information may be stored on the“data islands” and, in fact, may be defined by the frequency andpositioning of the data islands themselves.

[0050] In an alternative embodiment, the troughs of the patterned mediummay contain data, such as servo information. The servo information maybe written to the bottom surface (or “floor”) of the troughs (asmagnetic transitions) at a lower frequency than the data written to thelands. For example, the servo information may be written at 1 MegaHertz(MHz) and the data on the lands may be written at 19 to 250 MHz. Writingthe data and servo at these or other frequencies allows a read element,such the read element on read wide/write narrow recording head 80, tosense both data and servo information.

[0051] In more detail, the recording head is able to sensehigh-frequency data at a close distance. The recording head is also ableto sense lower-frequency data at a farther distance. Accordingly, thedata on the lands, which is closer to the recording head, can be writtenat a high frequency and the servo information in the troughs, which isfarther away from the recording head, can be written at a lowerfrequency. Thus, the recording head can sense both simultaneously at thesame flight height. In this embodiment, the read element is wider thanthe land and, accordingly, extends over the lands and into the troughson either side of the land, allowing the read element to sense both thedata and servo information.

[0052] The equation that governs the readability of data relative to theheight of the recording head above the recording medium is called theWallace equation. The Wallace equation is as follows:${FH} = {\frac{\lambda}{2\pi}{{l_{n}\left( \frac{V_{1}}{V_{h}} \right)}.}}$

[0053] In the Wallace equation, “FH” is the flying height of therecording head, i.e., the distance above the recording medium; “λ” isthe wavelength in distance between two magnetic transitions that definedata; “V_(l)” is the amplitude of the low flying height of the readelement above the data magnetic transitions on the recording medium ofthe lands; “V_(h)” is the amplitude of the high flying height of theread element above the servo magnetic transitions in the troughs; and“ln” is the natural logarithm function.

[0054] The flying height (FH) that enables the read element to read lowfrequency magnetic transitions in the troughs is determined by solvingthe Wallace equation. The Wallace equation may also be used to confirmthat the read element is able to sense the high frequency magnetictransitions (i.e., the data) on the lands.

[0055] Moreover, because the data (as opposed to the servo information)is written at a high frequency, the write element will not be able towrite data in the troughs. As a result, the troughs are still able toact as effective erase bands.

[0056] Instead of writing the servo information onto a smooth surfacedtrough, patterned steps may be physically formed in the trough. Theservo information includes the patterned steps, which create lowfrequency signals by the abrupt changes in magnetization created by thesteps themselves. FIG. 7 shows an example of using patterned steps tostore servo information (or even other data) in the troughs of apatterned magnetic recording medium 110.

[0057] In the example of FIG. 7, the lands and troughs comprisealternating concentric tracks of a magnetic disk; however, the inventionis not limited as such. As noted, the lands and troughs may be spiralsor have any other configuration. Lands 112 a, 112 b and 112 c may beused to store data, as described with respect to FIG. 5 above. The landsmay also include data islands, as shown in FIG. 6 above. Here, troughs114 a, 114 b, 114 c and 114 d contain two levels—a “floor” level 116 andsteps 118, as depicted in FIG. 8 (the lines 120 in FIG. 5 indicate thedepth differences in the troughs). The steps have a height, relative tofloor 116, that is less than the height of the lands. Servo informationincludes the steps, as above, positioned at a lower frequency than datais written onto the lands.

[0058] If the floor 116 of a trough is deep enough and the frequency ofthe steps is low enough, the servo information will be lower inbandwidth than the data, but still readable by the read element of therecording head. The Wallace equation is used to determine the flyingheight of the recording head relative to the steps and the lands and thefrequencies of the data and servo information.

[0059] The servo information stored in the troughs (either on patternedsteps or as magnetic transitions on the “floor”) is at differentfrequencies on either side of a land. As shown in FIG. 7, the servoinformation (on each of the patterned steps) is at a higher frequency intrough 114 b to the left of land 112 b than the servo information intrough 114 c to the right of land 112 b. The difference in frequenciesof the servo information permits continuous servo of the recording head.That is, a controller (not shown) takes the difference in the amplitudebetween the servo information from trough 114 b and the servoinformation from trough 114 c. The magnitude of this differenceindicates whether the recording head is veering too far towards onetrough or the other. In such an event, the controller adjusts theposition of the recording head to compensate for the unwanted veering.The head is on-track when the amplitudes of the signals from 114 b and114 c are equal.

[0060] The servo information written to the troughs may include servosignals and/or grey code. The servo signals include data that is used toascertain the position of the recording head. The grey code is data thatdefines the track addresses of data tracks on the magnetic recordingmedium.

[0061] In operation, as a recording head 120 moves over a land 112 b,the read element (not shown) of the recording head senses servoinformation in troughs 114 b and 114 c that border the land 112 b on theleft and right, respectively. The read element reads the servoinformation from the troughs along with the data from the lands.Referring to FIG. 9, the servo information and data is transmitted fromthe read element 120 to a preamplifier 122. Preamplifier 122 amplifiesthe signals read by the read head and transmits the amplified signals toa lowpass filter 124 and a highpass filter 126.

[0062] The lowpass filter 124 transmits low frequency servo informationfrom troughs 114 b and 114 c to the controller. The controller compares(e.g., takes the difference between) the servo information from trough114 b and the servo information from trough 114 c. The controllercompares the resulting difference value to one or more preset values inorder to determine if the recording head has veered too much into onetrough or other. If so, the controller issues a signal to correct theposition of the recording head.

[0063] The highpass filter 126 receives the output of preamplifier 122and passes high-frequency signals only, i.e., data from the lands andPLL (phase locked loop) information (which is timing information thatmay be contained in dedicated data sectors on the magnetic recordingmedium).

[0064] By storing servo information and grey code in the troughs, thesize of dedicated data sectors can be increased relative to recordingmedia that also store the servo information and the grey code indedicated data sectors. As a result, there is more room on the recordingmedium for data.

[0065] The invention is not limited to the specific embodiments setforth above. The different features of the various embodiments can becombined. For example, the data islands of FIG. 6 may be combined withthe stepped troughs of FIG. 7 in a single patterned magnetic recordingmedium. The stepped trough magnetic recording medium may be formed inthe same manner as the other patterned media described above. In thisregard, the patterned medium is not limited to a polymer layer on aglass substrate. Any type of imprintable magnetic recording material maybe used. The patterned medium is not limited to magnetic disks or otherrotatable media. The patterned medium may be magnetic tape or the like.

[0066] Other embodiments not specifically described herein are alsowithin the scope of the following claims.

What is claimed is:
 1. A magnetic recording disk, comprising: a substrate comprising aluminum; a magnetic recording layer; and a silica gel layer disposed between the substrate and the magnetic recording layer.
 2. The magnetic recording disk of claim 1, further comprising a NiP layer disposed between the substrate and the silica gel layer.
 3. A disk drive, comprising: a magnetic recording disk comprising an aluminum substrate, a magnetic recording layer, and a silica gel layer disposed between the substrate and the magnetic recording layer; and a recording head to transfer data to and from the magnetic recording disk.
 4. The disk drive of claim 3, wherein the magnetic recording disk further comprises a NiP layer disposed between the substrate and the silica gel layer.
 5. A method, comprising: producing a substrate comprising aluminum; disposing a silica gel layer above the substrate; and depositing a magnetic layer above the silica gel layer.
 6. The method of claim 5, further comprising disposing a NiP layer between the substrate and the silica gel layer. 